Hydraulic tool or edge grip clamps are known in the art, such as disclosed in U.S. Pat. Nos. 4,406,445 dated Sep. 22, 1983 and 4,410,169 dated Oct. 18, 1983. In the first of such patents the toe member of a low-profile toe clamp is advanced down an incline at the working end of the clamp by a pair of horizontal hydraulic pistons, one on each side of the hold-down slot of the clamp. The toe member is provided with transverse pins which are overridenly engaged by inclined faces on the pistons, so that the horizontal movement of the pistons is translated to the inclined movement of the toe member and so that a stopping action is provided by eventual engagement of the pistons with the toe member. Retraction is effected by a compression spring reacting between the toe member and the clamp body.
The second of such patents discloses a work holding clamp with double-acting hydraulically actuated jaw, wherein the forward end of the body member has a formed dovetail in which moves a jaw member at a selected slant or slope. Within the body member is a reciprocal hydraulic piston having its forward end formed with two cam surfaces. A lower cam surface is adapted to engage a mating cam surface on the jaw to move the jaw member forwardly and downwardly to a gripping condition. An actuation of the piston rearwardly causes an upper cam surface to engage a removable pin to move the upper jaw member upwardly and rearwardly to disengage the jaw member from the workpiece.
In each of the foregoing Patents, inclined cam surfaces of constant angle are employed in advancing the clamping jaw to workpiece engaging position, with reaction forces imposing a corresponding side loading component on the actuating piston which contributes to frictional resistance and wear on the bearing surfaces of such piston.